While some work toward an invisibility cloak, University of Illinois professor Nicholas Fang is taking steps to create a similar material, only for sound, that could, for example, make ships invisible to SONAR. To successfully do this, of course, requires we break the laws of physics. But, you know, whatever.

I'll let the experts explain:

Using conventional lenses, it's not possible to focus light waves or sound waves to a spot size smaller than half the wavelength of the light. To get around these limitations, a lens must refract, or literally bend light backward. No naturally occurring materials have a negative index of refraction, but some materials carefully designed in the lab, called metamaterials, do.

Fang, a mechanical science professor at the University of Illinois at Urbana-Champaign, is using an array (pictured above) of specially shaped, water-filled cavities in a piece of aluminum, which supposedly work together to refract the sound by resonating in a particular way. It's all sort of unclear, and nobody has yet figured out how to get around that whole wavelength issue, but this could be the start of even crazier stealth technology, which is always fun to see—or not see. Get it? Because it's stealth. [Technology Review]